Conventional batteries or electric cells are devices that convert chemical energy into electricity. Most conventional batteries consist of a liquid or a moist electrolyte and an external electric circuit connected between a positive and negative electrode. The electrolyte, a liquid or paste in which a dissolved chemical will dissociate into negative and positive ions, may be a solution of salts, acids or bases; a weak acid solution is commonly used because it conducts electricity for a longer time. The conventional electrodes are usually made of substances that will also dissociate in the electrolyte. Batteries in which the chemicals cannot be reconstituted into the original form once the energy has been converted, that is batteries that cannot be recharged, are called primary cells or voltaic cells. Batteries in which the chemicals can be reconstituted by passing an electric current through the electrolyte in the direction opposite that of the normal cell operation are called secondary cells, storage cells, or accumulators.
The most common form of primary cell is the Leclanche cell. This type of battery is commonly called a dry cell or flashlight battery. The conventional dry cell battery in use today is very similar to the original invention. The negative electrode is made of zinc, as is the outside shell of the cell, and the positive electrode is a thin carbon rod surrounded by a mixture of carbon and manganese dioxide. The dry cell normally produced about 1.5 volts.
Another widely used conventional primary cell is the zinc mercuric oxide cell, more commonly called a mercury battery. It can be made in the shape of a small, flat disc and is used in this form in hearing aids, photoelectric cells, and electric wrist watches. The negative electrode consists of zinc, the positive electrode is of mercuric oxide, and the electrolyte is a solution of potassium hydroxide. The mercury battery commonly produces about 1.34 volts. Secondary cells or rechargeable batteries include the lead acid storage battery. The lead acid battery which consists of three or six cells connected in series, is used in automobiles, trucks, aircraft and other vehicles. Its chief advantage is that it can deliver a strong current of electricity for starting an engine; however, it runs down quickly. The electrolyte is a dilute solution of sulfuric acid, the negative electrode consists of lead, and the positive electrode of lead dioxide. In operation, the negative lead electrode dissociates into free electrons and positive lead ions. The electrons travel through the external electric current and the positive lead ions combine with the sulfate ions in the electrolyte to form a lead sulfate. When the electrons re-enter the cell at the positive lead dioxide electrode, another chemical reaction occurs. The lead dioxide combines with the positive hydrogen ions in the electrolyte and with the returning electrons to form water, releasing lead ions in the electrolyte to form additional lead sulfate.
The lead acid storage cell runs down as the sulfuric acid gradually is converted into water and lead sulfate. When the cell is being recharged, the chemical reactions described above are reversed until the chemicals have been restored to their original condition. A lead acid battery has a useful life of about four years. It produces about two volts per cell.
Another widely used conventional secondary cell is the alkaline cell, or nickel-iron battery, developed by the American inventor, Thomas Edison, in the 1900s. The principle of operation is the same as the lead acid cell except that the negative electrode consists of iron, the positive electrode is of nickel-oxide, and the electrolyte is a solution of potassium hydroxide. The alkaline cell is more expensive than the lead acid battery, and the nickel iron cell has the additional disadvantage of giving off hydrogen gas during charging. The battery is used principally in heavy industry because it can stand rough treatment better than the lead acid batteries, which tend to leak acid. The alkaline cell has a useful life of approximately ten years and produces about 1.15 volts.
Another alkaline cell is the nickel-cadmium cell, or cadmium battery, in which the iron electrode is replaced by one consisting of cadmium. It also produces about 1.15 volts, and its useful lifetime is about twenty-five years. Recent research has yielded several new types of batteries primarily designed for use in electrical vehicles. Improved versions of conventional storage batteries have been developed for electric cars, but they still suffer the drawbacks of either short range, high expense, bulkiness, or extensive environmental problems. Batteries which show promise for use in electrical vehicles include lithium-iron sulfide, zinc chloride, and sodium sulfur. These batteries are also being developed by electric utilities to be used for load leveling as a reserve to respond quickly to additional demands, and to compensate for momentary system load fluctuations. Such battery modules can be installed close to sites of fluctuating demand and are independent of each other.
Finally, another class of batteries are the solar batteries. Solar batteries produce electricity by photoelectric conversion process. The source of electricity is a photosensitive semiconducting substance such as a silicon crystal to which impurities have been added. When the crystal is struck by light, electrons are dislodged from the surface of the crystal and migrate toward the opposite surface. There they are collected as a current of electricity. Solar batteries have very long lifetimes and are used chiefly in spacecraft as a source of electricity to operate the equipment load. Solar batteries are also being used to power vehicles. However, current solar batteries are relatively inefficient and only produce electricity when struck by strong light such as sunlight.
All of the conventional batteries suffer from serious drawbacks. Another problem with conventional batteries is in recharging the battery. Normally, a battery is recharged by forcing a current into the battery. However, this technique, while simple, can cause excessive heating of the battery, excessive gassing and require a prolonged time to fully recharge the battery.
A rechargeable battery, once discharged, requires recharging to restore energy to the battery. Several hours, or more, are typically required to recharge a battery because a conventional battery recharger cannot deliver a high charging current without causing overheating of the battery. As is well known in the art, overheating a battery dramatically reduces the life of the battery.
Another problem with conventional batteries is that they require formatting. Depending on the size and type of the battery, this may require twelve hours to several days. The electrolyte is placed in the battery and some electrolyte is absorbed by the plates. The initial chemical reaction generates a great deal of heat, and the battery temperature may easily reach 170.degree. F. Once the electrolyte is absorbed by the plates, the temperature will begin to fall, thereby indicating that the absorption (pickling) time is over, and the battery is ready for formation. An electrolyte temperature of 135.degree. F. to 145.degree. F. is desirable for battery formation.
Finally, a serious problem with any of the conventional-type batteries, is the gradual decrease in efficiency after charging. What is needed in the industry is an electrical storage device that is rapidly rechargeable, has no environmentally unsafe components, or chemicals, and is light weight.